Rosalind R. James

Mechanisms by which pesticides affect insect immunity.

The current state of knowledge regarding the effect of pesticides on insect immunity is reviewed here. A basic understanding of these interactions is needed for several reasons, including to improve methods for controlling pest insects in agricultural settings, for controlling insect vectors of human diseases, and for reducing mortality in beneficial insects. Bees are particularly vulnerable to sublethal pesticide exposures because they gather nectar and pollen, concentrating environmental toxins in their nests in the process. Pesticides do have effects on immunity. Organophosphates and some botanicals have been found to impact hemocyte number, differentiation, and thus affect phagocytosis. The phenoloxidase cascade and malanization have also been shown to be affected by several insecticides. Many synthetic insecticides increase oxidative stress, and this could have severe impacts on the production of some antimicrobial peptides in insects, but research is needed to determine the actual effects. Pesticides can also affect grooming behaviors, rendering insects more susceptible to disease. Despite laboratory data documenting pesticide/pathogen interactions, little field data is available at the population level.

Standard methods for research on Apis mellifera gut symbionts

Summary Gut microbes can play an important role in digestion, disease resistance, and the general health of animals, but little is known about the biology of gut symbionts in Apis mellifera. As part of the BEEBOOK series describing honey bee research methods, we provide standard protocols for studying gut symbionts. We describe non-culture-based approaches based on Next Generation Sequencing (NGS), methodology that has greatly improved our ability to identify the microbial communities associated with honey bees. We also describe Fluorescent In Situ Hybridization (FISH) microscopy, which allows a visual examination of the microenvironments where particular microbes occur. Culturing methods are also described, as they allow the researcher to isolate particular bacteria of interest for further study or gene identification, and enable the assignment of particular functions to particular gut community members. We hope these methods will help others advance the state of knowledge regarding bee gut symbionts and the role they play in honey bee health.

Field Evaluation of Beauveria bassiana: Its Persistence and Effects on the Pea Aphid and a Non-target Coccinellid in Alfalfa

Several strains of the entomopathogenic fungus Beauveria bassiana have been considered for use as microbial insecticides. Experimental sprays were conducted in an alfalfa field with an aphid-derived strain of B. bassiana to determine its persistence and its effects on pea aphids, Acyrthosiphon pisum (Homoptera: Aphididae) and a non-target aphid predator, Hippodamia convergens (Coleoptera: Coccinellidae). B. bassiana conidia persisted in the field for at least 28 days, when approximately 10% of the original inoculum was still present. In the lower canopy, more conidia were present than on other plant parts and they persisted longer on the leaves in this location. However, conidia were still abundant in the upper canopy, where 97.9% of the aphids and 95.5% of H. convergens larvae were found. Thus, both insect species were exposed to the fungus for at least 1 month. However, pea aphid populations were not affected by the fungus. The predators incidence was reduced by 75-93% (depending on application rate) e...

Antagonism Between Beauveria bassiana and Imidacloprid When Combined for Bemisia argentifolii (Homoptera: Aleyrodidae) Control

Abstract Imidacloprid and the entomopathogenic fungus Beauveria bassiana (Balsamo) Vuillemin are both used to control the whitefly Bemisia argentifolii Bellows & Perring. We tested whether the two control strategies acted additively, synergistically, or antagonistically when combined for whitefly control. We found antagonism in that B. bassiana inhibited the effectiveness of imidacloprid. When B. bassiana was combined with imidacloprid, insect response was either less than or similar to (depending on B. bassiana rates) that when imidacloprid was used alone. Adding imidacloprid to B. bassiana treatments always increased mortality, but the increase was less than additive. Beauveria bassiana spore germination and colony formation were not inhibited by imidacloprid in vitro, and B. bassiana did not adsorb or degrade imidacloprid in a tank mix. We hypothesize that B. bassiana caused a behavioral response that reduced insect feeding and uptake of imidacloprid.

Temperature dependent virulence of obligate and facultative fungal pathogens of honeybee brood

Chalkbrood (Ascosphaera apis) and stonebrood (Aspergillus flavus) are well known fungal brood diseases of honeybees (Apis mellifera), but they have hardly been systematically studied because the difficulty of rearing larvae in vitro has precluded controlled experimentation. Chalkbrood is a chronic honeybee-specific disease that can persist in colonies for years, reducing both brood and honey production, whereas stonebrood is a rare facultative pathogen that also affects hosts other than honeybees and can likely survive outside insect hosts. Hive infection trials have indicated that accidental drops in comb temperature increase the prevalence of chalkbrood, but it has remained unclear whether virulence is directly temperature-dependent. We used a newly established in vitro rearing technique for honeybee larvae to test whether there are systematic temperature effects on mortality induced by controlled infections, and whether such effects differed between the two fungal pathogens. We found that increasing spore dosage at infection had a more dramatic effect on mortality from stonebrood compared to chalkbrood. In addition, a 24h cooling period after inoculation increased larval mortality from chalkbrood infection, whereas such a cooling period decreased mortality after stonebrood infection. These results raise interesting questions about honeybee defenses against obligate and facultative pathogens and about the extent to which stress factors in the host (dis)favor pathogens with lesser degrees of specialization.

Detoxification and stress response genes expressed in a western North American bumble bee, Bombus huntii (Hymenoptera: Apidae)

BackgroundThe Hunt bumble bee (Bombus huntii Greene, Hymenoptera: Apidae) is a holometabolous, social insect important as a pollinator in natural and agricultural ecosystems in western North America. Bumble bees spend a significant amount of time foraging on a wide variety of flowering plants, and this activity exposes them to both plant toxins and pesticides, posing a threat to individual and colony survival. Little is known about what detoxification pathways are active in bumble bees, how the expression of detoxification genes changes across life stages, or how the number of detoxification genes expressed in B. huntii compares to other insects.ResultsWe found B. huntii expressed at least 584 genes associated with detoxification and stress responses. The expression levels of some of these genes, such as those encoding the cytochrome P450s, glutathione S-transferases (GSTs) and glycosidases, vary among different life stages to a greater extent than do other genes. We also found that the number of P450s, GSTs and esterase genes expressed by B. huntii is similar to the number of these genes found in the genomes of other bees, namely Bombus terrestris, Bombus impatiens, Apis mellifera and Megachile rotundata, but many fewer than are found in the fly Drosophila melanogaster.ConclusionsBombus huntii has transcripts for a large number of detoxification and stress related proteins, including oxidation and reduction enzymes, conjugation enzymes, hydrolytic enzymes, ABC transporters, cadherins, and heat shock proteins. The diversity of genes expressed within some detoxification pathways varies among the life stages and castes, and we typically identified more genes in the adult females than in larvae, pupae, or adult males, for most pathways. Meanwhile, we found the numbers of detoxification and stress genes expressed by B. huntii to be more similar to other bees than to the fruit fly. The low number of detoxification genes, first noted in the honey bee, appears to be a common phenomenon among bees, and perhaps results from their symbiotic relationship with plants. Many flowering plants benefit from pollinators, and thus offer these insects rewards (such as nectar) rather than defensive plant toxins.

Heterorhabditis mexicana n. sp. (Rhabditida: Heterorhabditidae) from Tamaulipas, Mexico, and morphological studies of the bursa of Heterorhabditis spp.

Summary – A new species of nematode in the genus Heterorhabditis was found in the northern part of the state of Tamaulipas, Mexico. Morphological and molecular data indicate that this nematode is a new species. The new species is described as Heterorhabditis mexicana n. sp. and is a sister taxon to H. indica. Heterorhabditis mexicana n. sp. is morphologically similar to H. bacteriophora, H. brevicaudis and H. indica and can be distinguished from these species mainly by male and female characters. Of the examined specimens of H. mexicana n. sp., 70% of males have eight pairs of bursal papillae, compared to nine in all other species. The ratio of the gubernaculum to spicule length (GS ratio) is higher than that of H. bacteriophora, H. brevicaudis and H. indica and the length of the spicule relative to anal body width (SW) is lower than all other species. For females, the vulval form of the new species is quite different from that of those species with a similar morphology (i.e., H. bacteriophora and H. indica) and more closely resembles that of H. zealandica. The new species can also be distinguished from H. megidis, H. zealandica and H. marelatus by the body length, pharynx length of the infective juvenile and D% (distance from anterior end/pharynx length ×100), GS and SW ratios of males. In the ITS region of the rDNA tandem repeating unit, H. mexicana n. sp. has evolved 13 autapomorphic nucleotide character states, differing from its sister taxon H. indica at 113 aligned positions. The morphological and molecular data are sufficient to identify cladogenesis and delimit H. mexicana n. sp. as evolving independently from the other members of the genus.

Do Weather Conditions Correlate with Findings in Failed, Provision-Filled Nest Cells of Megachile rotundata (Hymenoptera: Megachilidae) in Western North America?

Abstract Cavity-nesting alfalfa leafcutting bees, Megachile rotundata (F.) (Hymenoptera: Megachilidae), are excellent pollinators of alfalfa, Medicago savita L., for seed production. In commercial settings, artificial cavities are placed in field domiciles for nesting and, thereby, bee populations are sustained for future use. For this study, cells from leafcutting bee nests were collected in late summer from commercial seed fields. Over 3 yr (2003–2005), 39 samples in total of ≈1,000 cells each were taken from several northwestern U.S. states and from Manitoba, Canada. X-radiography of 500 cells from each sample was used to identify “pollen balls” (i.e., cells in which the pollen–nectar provision remained, but the egg or larva, if present, was not detectable on an x-radiograph). Most U.S. samples seemed to have higher proportions of pollen ball cells than Manitoba samples. Pollen ball cells were dissected to determine the moisture condition of the mass provision and true contents of each cell. Most pollen ball cells from Manitoba samples contained fungus, the frequency of which was positively correlated with cool, wet weather. In the United States, most pollen ball cells had moist provisions, and many of them lacked young brood. Correlation analysis revealed that pollen ball cells occurred in greater proportions in fields with more hot days (above 38°C). Broodless pollen ball cells occurred in greater proportions under cool conditions, but dead small larvae (second–third instars) seemed to occur in greater proportions under hot conditions. Pollen ball cells with unhatched eggs and first instars (in the chorion) occurred in lesser proportions under hot conditions.

Ascosphaera subglobosa, a new spore cyst fungus from North America associated with the solitary bee Megachile rotundata

Ascosphaera subglobosa (Eurotiomycetes: Onygenales) is newly described from the pollen provisions and nesting material of the solitary leaf-cutting bee Megachile rotundata in Canada and the western United States. This new species, related to A. atra and A. duoformis, is distinguished from other Ascosphaera species by its globose to subglobose ascospores, evanescent spore balls and unique nuclear ribosomal DNA sequences (ITS and LSU).

Potential of Ozone as a Fumigant to Control Pests in Honey Bee (Hymenoptera: Apidae) Hives

ABSTRACT Ozone is a powerful oxidant capable of killing insects and microorganisms, and eliminating odors, taste, and color. Thus, it could be useful as a fumigant to decontaminate honey comb between uses. The experiments here are intended to determine the exposure levels required to kill an insect pest and spore forming bee pathogens. Ozone was effective against greater wax moth, Galleria mellonella (L.) (Lepidoptera: Pyralidae), even on naturally infested comb. Neonates and adults were the easiest life stages to kill, requiring only a few hours of exposure, whereas eggs required a 48-h exposure (at 460–920 mg O3/m3). Two honey bee, Apis mellifera L. (Hymenoptera: Apidae), pathogens, Ascosphaera apis (a fungus that causes chalkbrood) and Paenibacillus larvae (a bacterium that causes American foulbrood), also were killed with ozone. These pathogens required much higher concentrations (3,200 and 8,560 mg O3/m3, respectively) and longer exposure periods (3 d) than needed to control the insects. P. larvae was effectively sterilized only when these conditions were combined with high temperature (50°C) and humidity (≥75% RH). Thus, ozone shows potential as a fumigant for bee nesting materials, but further research is needed to evaluate its acceptability and efficacy in the field. The need for a reliable method to decontaminate honey bee nesting materials as part of an overall bee health management system is discussed.